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<meta name="description" content="页面中的很多效果都是动态发生改变的,比如:轮播图,每隔一定的时间都换一张图片显示，这些效果都可以用javascript的定时器实现。 间隔定时器,setInterval()setInterval(callback, delay);//每隔delay毫秒的时间就执行一次callback. 123456var si = setInterval(&quot;alert(&apos;helloworld&apos;)&quot;, 1000);">
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<meta property="og:description" content="页面中的很多效果都是动态发生改变的,比如:轮播图,每隔一定的时间都换一张图片显示，这些效果都可以用javascript的定时器实现。 间隔定时器,setInterval()setInterval(callback, delay);//每隔delay毫秒的时间就执行一次callback. 123456var si = setInterval(&quot;alert(&apos;helloworld&apos;)&quot;, 1000);">
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          <h2 class="post-title" itemprop="name headline">JavaScript定时器</h2>
        

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        <p>页面中的很多效果都是动态发生改变的,比如:轮播图,每隔一定的时间都换一张图片显示，这些效果都可以用javascript的定时器实现。</p>
<h2 id="间隔定时器-setInterval"><a href="#间隔定时器-setInterval" class="headerlink" title="间隔定时器,setInterval()"></a>间隔定时器,setInterval()</h2><p><code>setInterval(callback, delay);</code>//每隔delay毫秒的时间就执行一次callback.</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> si = setInterval(<span class="string">"alert('helloworld')"</span>, <span class="number">1000</span>);<span class="comment">//每隔1s输出helloworld</span></span><br><span class="line">function <span class="function"><span class="title">fun</span><span class="params">()</span></span>&#123;</span><br><span class="line">    console.log(<span class="string">"helloworld"</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">si = setInterval(<span class="function"><span class="keyword">fun</span>, 1000); //传入函数也可以，比较常用</span></span><br></pre></td></tr></table></figure>
<blockquote>
<p>注意：setInterval如果调用的程序在间隔的时间内没有完成，那么仍然会再次执行该函数.</p>
</blockquote>
<blockquote>
<p>注意:间隔定时器是异步代码,必须等全部同步代码加载完毕,他才会运行!</p>
</blockquote>
<blockquote>
<p>注意:间隔定时器中的时间,指的是多少毫秒之后去排队,不一定会立即执行.如果代码的运行时间要大于间隔时间,那么在时间队列中就会有很多该任务.</p>
</blockquote>
<h2 id="取消间隔定时器-clearInterval"><a href="#取消间隔定时器-clearInterval" class="headerlink" title="取消间隔定时器,clearInterval()"></a>取消间隔定时器,clearInterval()</h2><figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">function <span class="function"><span class="title">fun</span><span class="params">()</span></span>&#123;</span><br><span class="line">    console.log(<span class="string">"helloworld"</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> si = setInterval(<span class="function"><span class="keyword">fun</span>, 1000);</span></span><br><span class="line">clearInterval(si);<span class="comment">//需要用到setInterval返回的id</span></span><br></pre></td></tr></table></figure>
<h2 id="运用间隔定时器写一个简单的倒计时"><a href="#运用间隔定时器写一个简单的倒计时" class="headerlink" title="运用间隔定时器写一个简单的倒计时"></a>运用间隔定时器写一个简单的倒计时</h2><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE html&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">title</span>&gt;</span>timer<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">style</span> <span class="attr">media</span>=<span class="string">"screen"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="undefined">      *&#123;</span></span><br><span class="line"><span class="undefined">        border: 0;</span></span><br><span class="line"><span class="undefined">        padding: 0;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="css">        <span class="selector-class">.time</span>&#123;</span></span><br><span class="line"><span class="css">          <span class="selector-tag">width</span><span class="selector-pseudo">:400px</span>;</span></span><br><span class="line"><span class="undefined">          height: 300px;</span></span><br><span class="line"><span class="undefined">          font-size: 20px;</span></span><br><span class="line"><span class="undefined">          margin: 20px auto;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="css">        <span class="selector-class">.time</span> <span class="selector-tag">p</span>&#123;</span></span><br><span class="line"><span class="undefined">          text-align: center;</span></span><br><span class="line"><span class="undefined">          color: red;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">style</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">div</span> <span class="attr">class</span>=<span class="string">"time"</span>&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">p</span>&gt;</span>倒计时<span class="tag">&lt;<span class="name">span</span>&gt;</span>10<span class="tag">&lt;/<span class="name">span</span>&gt;</span>秒<span class="tag">&lt;/<span class="name">p</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">type</span>=<span class="string">"text/javascript"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="javascript">      <span class="keyword">var</span> time = <span class="built_in">document</span>.getElementsByClassName(<span class="string">'time'</span>)[<span class="number">0</span>];</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> timer = time.firstElementChild.firstElementChild;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> count = <span class="number">10</span>;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> fun = <span class="function"><span class="keyword">function</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="undefined">        count--;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">if</span>(count === <span class="number">0</span>)&#123;</span></span><br><span class="line"><span class="actionscript">          time.style.display = <span class="string">'none'</span>;</span></span><br><span class="line"><span class="actionscript">          clearInterval(timecount);<span class="comment">//记得要清理间隔计时器,不然会持续运行,占用大量内存.</span></span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="undefined">        timer.innerHTML = count;</span></span><br><span class="line"><span class="javascript">        <span class="built_in">console</span>.log(count);</span></span><br><span class="line"><span class="undefined">      &#125;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> timecount = setInterval(fun, <span class="number">1000</span>);</span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"></span><br><span class="line">  <span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h2 id="超时定时器-setTimeout"><a href="#超时定时器-setTimeout" class="headerlink" title="超时定时器,setTimeout()"></a>超时定时器,setTimeout()</h2><p><code>setTimeout(callback,delay);</code>间隔delay毫秒之后执行函数callback,并且只执行一次。</p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">outPut</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">        <span class="keyword">var</span> d = <span class="keyword">new</span> <span class="built_in">Date</span>();</span><br><span class="line">        <span class="built_in">console</span>.log(d.getSeconds());</span><br><span class="line">        num++;</span><br><span class="line">        <span class="keyword">if</span> (num == <span class="number">10</span>) &#123;</span><br><span class="line">            <span class="keyword">return</span>;</span><br><span class="line">        &#125;</span><br><span class="line">        setTimeout(<span class="built_in">arguments</span>.callee, <span class="number">1000</span>);<span class="comment">//1s之后再次运行outPut函数</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h2 id="取消超时定时器-clearTimeout"><a href="#取消超时定时器-clearTimeout" class="headerlink" title="取消超时定时器,clearTimeout()"></a>取消超时定时器,clearTimeout()</h2><p>与间隔定时器的取消定时器类似.</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE html&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">title</span>&gt;</span>timeout<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">type</span>=<span class="string">"text/javascript"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="actionscript">    <span class="keyword">var</span> count = <span class="number">5</span>;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> fun = <span class="function"><span class="keyword">function</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="undefined">        count--;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">if</span>(count == <span class="number">0</span>)&#123;</span></span><br><span class="line"><span class="undefined">          clearTimeout(out);</span></span><br><span class="line"><span class="actionscript">          <span class="keyword">return</span>;<span class="comment">//一定要return，不然下面有添加了新的定时器</span></span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="javascript">        <span class="built_in">console</span>.log(<span class="string">'呵呵'</span>);</span></span><br><span class="line"><span class="javascript">        <span class="built_in">console</span>.log(count);</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">var</span> out = setTimeout(fun, <span class="number">1000</span>);</span></span><br><span class="line"><span class="undefined">      &#125;</span></span><br><span class="line"><span class="undefined">      fun()</span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h2 id="超时定时器写一个倒计时"><a href="#超时定时器写一个倒计时" class="headerlink" title="超时定时器写一个倒计时"></a>超时定时器写一个倒计时</h2><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE html&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">title</span>&gt;</span>倒计时<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">style</span> <span class="attr">media</span>=<span class="string">"screen"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="undefined">      *&#123;</span></span><br><span class="line"><span class="undefined">        border: 0;</span></span><br><span class="line"><span class="undefined">        padding: 0;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="css">        <span class="selector-class">.time</span>&#123;</span></span><br><span class="line"><span class="css">          <span class="selector-tag">width</span><span class="selector-pseudo">:400px</span>;</span></span><br><span class="line"><span class="undefined">          height: 300px;</span></span><br><span class="line"><span class="undefined">          font-size: 20px;</span></span><br><span class="line"><span class="undefined">          margin: 20px auto;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="css">        <span class="selector-class">.time</span> <span class="selector-tag">p</span>&#123;</span></span><br><span class="line"><span class="undefined">          text-align: center;</span></span><br><span class="line"><span class="undefined">          color: red;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">style</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">div</span> <span class="attr">class</span>=<span class="string">"time"</span>&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">p</span>&gt;</span>倒计时<span class="tag">&lt;<span class="name">span</span>&gt;</span>10<span class="tag">&lt;/<span class="name">span</span>&gt;</span>秒<span class="tag">&lt;/<span class="name">p</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="javascript">      <span class="keyword">var</span> time = <span class="built_in">document</span>.getElementsByClassName(<span class="string">'time'</span>)[<span class="number">0</span>];</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> span = time.firstElementChild.firstElementChild;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> count = <span class="number">10</span>;</span></span><br><span class="line"><span class="actionscript">      <span class="function"><span class="keyword">function</span> <span class="title">fun</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="undefined">        count--;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">if</span>(count===<span class="number">0</span>)&#123;</span></span><br><span class="line"><span class="undefined">          clearTimeout(timeout);</span></span><br><span class="line"><span class="actionscript">          time.style.display = <span class="string">'none'</span>;</span></span><br><span class="line"><span class="actionscript">          <span class="keyword">return</span>;<span class="comment">//这里和间隔计时器不同,这里必须return,不然下面又会创建一个新的超时计时器.</span></span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="undefined">        span.innerHTML = count;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">var</span> timeout = setTimeout(fun, <span class="number">1000</span>);</span></span><br><span class="line"><span class="undefined">      &#125;</span></span><br><span class="line"><span class="undefined">      fun();</span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>

      
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